1. Field
Example embodiments of the present invention generally relate to a sheet conveying device effectively conveying various types of sheets, an image forming apparatus such as a copier, a facsimile machine, a printer, a printing machine, an inkjet recording device, a scanner provided with the sheet conveying device, and a multifunctional machine combining functions of at least two of the above.
2. Discussion of the Related Art
In order to reduce the overall sizes of related-art image forming apparatuses including copiers such as a PPC (plain paper copier) and an electrophotographic copier, facsimile machines, printers, printing machines, and inkjet recording devices, the sizes of conveying units provided therein also tend to be reduced.
Specifically, a conveying unit is used for conveying a recording medium or a sheet-type recording medium onto which an image is formed (hereinafter, referred to as “sheet”). The sheet is fed from a sheet storing unit or a sheet accommodating unit in which sheets are stacked and is conveyed to a main body of an image forming apparatus.
In reference to FIG. 1, example operations of an image forming apparatus and a sheet storing unit provided in the image forming apparatus are described.
FIG. 1 shows an example of a known monochrome copier 100 serving as an image forming apparatus.
The copier 100 in FIG. 1 includes a main body 102 thereof, a sheet feeding device 103 on which the main body 102 of the copier 100 is mounted, an image scanning device 104 attached on the main body 102 of the copier 100, a sheet eject tray 109, a fixing device 111, a transfer device 113, and a sheet reversing device 142.
The main body 102 of the copier 100 includes an image forming section for performing a given image forming process based on a scanned original image.
The sheet feeding device 103 supplies one sheet S at a time to the main body 102 of the copier 100. The sheet feeding device 103 includes a sheet conveying device 105. The sheet conveying device 105 includes a first conveying unit 106 and a second conveying unit 107 and is configured to feed and convey the sheets S stored in sheet feeding cassettes 151 of the sheet feeding device 103.
The image scanning device 104 scans an original image and sends information of the original image to the main body 102 of the copier 100.
The sheet eject tray 109 receives and holds (or stacks) sheets that have passed through the main body 102 of the copier 100.
The fixing device 111 fixes a transferred toner image onto a sheet.
The transfer device 113 transfers a toner image from a circumferential surface of a photoconductor 110A of an image forming device 110 onto a sheet, and conveys the sheet to which an unfixed toner image is transferred to the downstream side of a sheet conveying path Ra of the sheet reversing device 142.
The sheet reversing device 142 conveys a sheet back and forth along the sheet conveying path Ra and/or a sheet conveying path Rb and a reverse conveying path Rc to reverse the sides of the sheet S.
In the copier 100 of FIG. 1, a pickup roller 160 picks up a sheet S placed on top of a stack of sheet stacked and stored in one of the sheet feeding cassettes 151. When two or more sheets S are picked up by the pickup roller 160, one sheet in contact with a feed roller 161 of the first conveying unit 106 is separated from the other sheet(s) in contact with a reverse roller 162 of the first conveying unit 106. Then, the sheet S separated and fed by the feed roller 161 is conveyed to a pair of grip rollers 181 of the second conveying unit 107 disposed in a downstream side of the first conveying unit 106. The sheet S conveyed to the pair of grip rollers 181 abuts a leading edge thereof against a position immediately before a nip contact of a pair of registration rollers 121 disposed at a downstream side in a travel direction of the sheet S. When the leading edge of the sheet S abuts against the above-described position, the sheet S stops to change its position so as to provide a given bend at the leading edge thereof and to prevent skew or positional instability thereof. At a given timing in synchronization with a completion of an image forming operation on the photoconductor 110A, the pair of registration rollers 121 again starts to convey the sheet S to the transfer device 113.
The copier 100 of FIG. 1 employs a feed reverse roller (FRR) sheet separation mechanism, which uses a return separating method. However, a mechanism of separating and feeding a sheet at a separation position is not limited to the FRR sheet separation mechanism. For example, a sheet separation mechanism using a frictionally resisting member or a friction pad sheet separation mechanism that has a simple and inexpensive configuration can be applied to the sheet separation mechanism for the copier 100 of FIG. 1.
To reduce a time period from which the sheet S is fed from the sheet feeding cassette 151 to which the sheet S is ejected to the sheet eject tray 109, the sheet conveying path Ra extending from the sheet feeding device 103 to the fixing device 111 is directed to a substantially vertically upward direction or a direction substantially perpendicular to a horizontal direction.
A common conveying path is also provided so that the reversed sheet S can be conveyed through the reverse conveying path Rc of the sheet revering device 142 to the pair of registration rollers 121.
Further, a manual sheet feeding tray 167 is provided outside the main body 102 of the copier 100, below the reverse conveying path Rc. The manual sheet feeding tray 167 includes a sheet feeding roller 167A, and separating rollers 167B and 167C. The sheet S fed from the manual sheet feeding tray 167 is conveyed toward the pair of grip rollers 181 provided in the vicinity of the upper one of the sheet feeding cassettes 151. Accordingly, the common conveying path is provided before the pair of grip rollers 181 of the upper sheet feeding cassettes 151.
In recent years, a shorter distance from the sheet feeding device 103 to the pair of registration rollers 121 is highly demanded to further reduce the size of the copier 100. To meet the demand, a removal of the pairs of grip rollers 181 from the vicinity of the upper and lower sheet feeding cassettes 151 of the sheet feeding device 103 is taken into consideration.
The inventors of the present application therefore conducted a test to evaluate a sheet feeding operation after removing the pairs of grip rollers 181 from the sheet feeding device 103. Consequently, the inventors found that the removal of the pair of grip rollers 181 decreased a sheet conveying force of the sheet S, increased a slip rate of the sheet S, and caused a paper jam to occur before the pair of grip rollers 181. The evaluation resulted in a decrease of reproduction of copies or prints. The inconvenience was more obvious especially when a relatively high rigid sheet such as a cardboard recording medium was conveyed. According to the test result, the inventors of the present invention found the pair of grip rollers 181 is necessary to the copier 100.
Furthermore, the related-art image forming apparatuses generally accommodate various sheet sizes and sheet types. For example, sheets of different sizes and different types are previously stored in multiple sheet storing units. A sheet is fed from the sheet storing unit selected by a user or automatically selected by an image forming apparatus. In such a configuration, each sheet storage unit occupies a large space in the related-art image forming apparatus, and therefore, it is particularly necessary to reduce the size of the related-art conveying unit.
One approach is to have a conveying path between the sheet storing unit and a main body of a related-art image forming apparatus that considerably bends or changes its direction midway depending on the relative positions of the sheet storing unit and the main body, so as to reduce the space occupied by the conveying path. Thus, in order to change the conveying direction in a continuous and smooth manner in the conveying path, the conveying path is provided with a curved section. The curved section includes a relatively small curvature radius so that a regular-sized recording sheet normally used in the related-art image forming apparatus can be conveyed.
In one technique or a first technique used in a sheet feeding device of a related-art image forming apparatus, sheet feed trays serving as sheet storing units are arranged beneath a main body of an image forming apparatus. Given numbers of sheets of given sheet sizes and sheet types are stacked in the sheet storing units. In between the sheet storing units and the main body of the related-art image forming apparatus, a sheet conveying unit is provided for extracting a sheet in a substantially horizontal direction from the selected sheet storing unit and feeding the extracted sheet in an upward direction toward the main body of the image forming apparatus disposed above.
A sheet in a sheet storing unit is separated from the stack of sheets by a related-art FRR (Feed Reverse Roller) sheet separation mechanism, and is sent to the main body of the image forming unit through a conveying path provided with a curved section including an upper guide plate and a lower guide plate, each of which serves as a guide member for fixing a curved section. As the sheet is conveyed further on, the sheet is pressed from above by the upper guide plate. The sheet is conveyed by an elastically deformable guide piece positioned at the outlet end of the lower guide plate and reaches a pair of conveying rollers. Hereinafter, the upper guide plate and the lower guide plate are referred to as the “guide member for fixing a curved section.”
However, in the sheet conveying device with the above-described configuration, the following problem arises when conveying a specific type of sheet with high rigidity, such as a cardboard recording paper or an envelope. That is, when the sheet bends and moves along the curved section, such a highly rigid recording paper or special paper receives a much greater resistance compared to a regular sheet such as a plain paper used for copying. This is because the curved section in the conveying path has a small radius. As a result, the highly rigid sheet cannot smoothly move along the conveying path, causing a paper jam or a conveyance failure. Thus, the sheet feeding operation cannot be reliably performed.
In order to facilitate the understanding of the related art and its problems, a description is now given of further details of the above-described conveyance operation.
When the leading edge of the sheet in the sheet conveying direction reaches the guide member for fixing a curved section configured with the upper guide plate and the lower guide plate, the front half of the sheet including the leading edge of the sheet curves or bends in its thickness direction. Accordingly, when a highly rigid sheet is conveyed, a large force resists this bending action, in such a manner that a large resistance obstructs the sheet conveying operation. As a result, the leading edge of the highly rigid sheet may not reach the pair of conveying rollers at the downstream side of the sheet conveying direction, with the result that the sheet may be conveyed only by a pair of rollers on the upstream side thereof. However, when the sheet is bent by the guide member, the conveying force of the pair of rollers alone may be insufficient for conveying the highly rigid sheet to counter to the resistance caused by the bending action. As a result, the following conveyance failures may be caused. Specifically, the sheet is caused to move in an oblique manner because the center-line of the highly rigid sheet does not match the center-line of the conveying path, or a paper jam occurs because the highly rigid sheet is caught inside the guide member and stops moving.
Accordingly, the above-described sheet feeding device with the first technique has been proposed. In the sheet feeding device, a sheet is sent out from a first conveying member then conveyed to a second conveying member disposed at a position downstream in the conveying direction and substantially vertically above the first conveying member. A pair of linear guide members is provided between the first conveying member and the second conveying member, and the sheet is conveyed by being guided by these linear guide members. In this sheet feeding device, the guide members do not have curved shapes but have linear shapes, and therefore, the conveyance load can be maintained at a low level. That is, the load can be prevented from rising abruptly so that conveyance failures such as a paper jam or oblique movements can be prevented.
That is, according to the above-described sheet feeding device, the conveyed sheet is not deformed or bent only at one position, but is deformed at two positions, i.e., near the front and the back ends of the linear guide members in the sheet conveying direction. Furthermore, the linear guide members are disposed obliquely at substantially intermediate angles, so that the sheet may bend by the same amount at the above-described two positions. Therefore, the conveyance load is prevented from rising abruptly. Specifically, the sheet changes its traveling direction by bending at the two positions, namely, when the sheet is passed from the pair of rollers located at the upstream side of the sheet conveying or traveling direction to the linear guide member, and when the sheet is passed from the linear guide member to the pair of rollers located at the downstream side of the traveling direction. Thus, the sheet bends by smaller extents at these two positions than when the sheet abruptly bends at one position only. Thus, the resistance caused by the bending action of the sheet can be reduced at each of the two positions, thereby preventing the conveyance load from rising abruptly.
Another type of sheet feeding device with a first conveying member and a second conveying member having substantially the same configurations as the above-described sheet feeding device employing the first technique is described as follows.
This sheet feeding device employing another technique or a second technique includes a reverse guiding member provided at an incline between the first conveying member and the second conveying member. This reverse guiding member is configured to move toward the second conveying member.
In this sheet feeding device, when the trailing edge of the sheet contacts the reverse guiding member, the reverse guiding member shifts its position in a direction substantially according to the trailing edge of the sheet. This shift makes it possible to absorb the shock or impact caused when the trailing edge of the sheet contacts the reverse guiding member. Hence, a flipping noise can be reduced.
Yet another type of sheet feeding device with a technique or a third technique different from the first and second techniques has been proposed. This sheet feeding device employing the third technique includes multiple sheet storing units for storing sheets, and each of the sheet storing units is provided with a conveying path and a sheet conveying unit. The ends of the conveying paths merge into a common conveying path. Each of the conveying paths has a curved section at the end thereof, at which each conveying path merges with the common conveying path. At least one of the conveying paths provided for a sheet storing unit that stores or accommodates highly rigid sheets has a first curved section with a larger curvature radius than those of the other conveying paths.
Therefore, in this sheet feeding device, highly rigid sheets are caused to bend more moderately compared to plain paper sheets. A highly rigid sheet moves along the conveying path and passes via the first curved section having a large curvature radius, so that the sheet may not bend as much as a plain paper sheet passing via a curved section having a smaller curvature radius. Accordingly, it is possible to reduce the resistance while conveying a highly rigid sheet, so that the sheet can be conveyed to the common conveying path without being suspended or stopped.
Now, a sheet reversing unit employing another technique is described. The sheet reversing unit is provided in a related-art image forming apparatus. This sheet reversing unit includes a pair of reverse rollers and a reverse conveying path for conveying and guiding a sheet received from the pair of reverse rollers. The reverse conveying path includes a redirection section for changing the direction of conveying a sheet. Rotatable members or rollers are arranged inside the redirection section in a direction orthogonal or perpendicular to the sheet conveying direction, so that a sheet sent into the reverse conveying path can be sent out while abutting the rollers.
According to this sheet reversing unit, when a sheet is sent inside, it is ensured that the portion of the sheet inside the redirection section contacts the rollers, and the rollers are caused to rotate by or following the movement of the sheet in the conveying direction. Thus, compared to a related-art guiding plate, the conveying resistance can be reduced. Specifically, it is possible to eliminate a frictional resistance occurring between a fixed guiding member and the moving sheet while changing the conveying direction of the sheet at the redirection section.
However, the technology used in the copier 100 in FIG. 1 may require the pair of grip rollers 181 to prevent paper jams that can occur before the pair of grip rollers 181. The configuration of the copier 100 with the pair of grip rollers 181 may degrade the sheet conveying properties for conveying relatively rigid sheets by reducing space at a turning or a curved section of a conveying path from the feed roller 161 and the reverse roller 162 of the first conveying unit 106 of the sheet feeding device 103 to the pair of grip rollers 181. As a result, especially when a relatively rigid sheet S such as a cardboard recording paper is conveyed, the leading edge of the sheet S may abut against a lower circumferential surface of an outer one, or a roller on the right side in FIG. 1, of the pair of grip rollers 181 and/or a distance from the pair of grip rollers 181 to the pair of registration rollers 121 may be reduced. Therefore, the sufficient space for bending the leading edge of the sheet S by abutting against the position immediately before the nip contact of the pair of registration rollers 121 cannot be obtained. Accordingly, skew and positional misregistration at the leading edge of the sheet S may be caused.
However, the sheet conveying device of the sheet feeding device using the first technique merely provides a fixed member for guiding a conveyed sheet, and thus does not eliminate the speed difference between the moving conveyed sheet and the fixed guiding member. Accordingly, regardless of the shape or position of the guiding member, resistance occurs in such a direction as to obstruct the sheet from being conveyed, which generating a conveyance load.
That is, this related-art configuration is insufficient for preventing conveyance failures or paper jams. Although the linear guiding member can reduce the conveyance load from rising abruptly, a conveyance load is generated nonetheless. Particularly when conveying a highly rigid sheet, such as a cardboard recording paper or an envelope, conveyance failures and paper jams frequently occur and flipping noises made by the trailing edge of the sheet increase considerably.
Furthermore, as described in reference to the sheet feeding device with the second technique, the reverse guiding member can shift or change its position in a direction according to the trailing edge of the sheet contacting the reverse guiding member. However, the reverse guiding member merely functions as a fixed guiding member in terms of changing the direction of the sheet. Accordingly, as with the related-art configuration described above, this related-art technique does not eliminate the relative speed difference between the sheet and the reverse guiding member when changing the direction of the sheet and guiding the sheet, thus generating a conveyance load. Particularly when conveying a highly rigid sheet, such as a cardboard recording paper or an envelope, conveyance failures and paper jams frequently occur and flipping noises caused by the trailing edge of the sheet increase considerably.
Furthermore, as described in reference to the sheet feeding device with the third technique, the conveying path with a large curvature radius dedicated to highly rigid sheets makes it possible for sheets traveling therethrough to bend moderately so as to reduce the conveyance resistance applied by the conveying path to the sheet. However, a conveyance load is still generated nonetheless, and therefore, particularly when conveying a highly rigid sheet, such as a cardboard recording paper or an envelope, conveyance failures and paper jams frequently occur.
Furthermore, as described in reference to the sheet reversing unit with the fourth technique, movable members such as rollers are provided at given positions inside the redirection section of the conveying path. Therefore, in the process of conveying the sheet, the frictional resistance between the sheet and the guiding member can be effectively reduced while the internal rollers are supporting the middle portion of the sheet between the leading edge and the trailing edge. However, there are no measures provided for reducing the conveyance load before and after the sheet is supported by the internal rollers, i.e., when the sheet is in contact with the conveying path outside the redirection section. Furthermore, no particular description is made of movements of the leading edge and the trailing edge of the sheet while being conveyed. Particularly when conveying a highly rigid sheet such as a cardboard recording paper or an envelope, conveyance failures and paper jams frequently occur and flipping noises caused by the trailing edge of the sheet increase considerably.